It should be noted that what are talking about here are specific kinds of adjectives, typically called demonstrative adjectives. Common adjectives are, of course, not declined in English to indicate number.
You would never say “blacks boots,” for example. It’s always going to be just “black boots,” even if there as many as a million green men involved. Thus, there is no agreement in number to worry about as to the form of the adjective. (In many other languages, of course, one is not so lucky.)
The demonstrative class of adjectives is a pretty small group. You have this, that, these, and those — and that’s it. Because their sole function is to specify, point to, or point out the specific thing or things (nouns) to which they refer, it kind of makes sense that their specificity would extend to number.
This, that, these, and those are called demonstrative pronouns when they are used as pronouns, that is, in place of noun instead of modifying one.
Shannon Wells
